Method of forming wire



Dec. 4, 1962 c. H. TOENSING 3,066,407

METHOD OF FORMING WIRE Filed March 17, 1958 1TWW-170T1 Clarence I-LToensing b3 M His AlTtOTTWQH.

United States Patent 3,066,407 METHOD OF FORMING WIRE Clarence H. Toensing, Lyndhurst, Ohio, assignor to General Electric Company, a corporation of New York Filed Mar. 17, 1958, Ser. No. 721,960

4 Claims. (Cl. 29-528) This invention relates to the production of wire and wire coatings, particularly of the more refractory metals, such as, e.g., tungsten and molybdenum, and to the continuous formation of wire and wire coatings by the slipcasting technique.

Briefly stated, according to the invention, a slurry is made from a metal powder and a fine wire is drawn therethrough so as to coat the wire. The slurry adhering to the wire is then dried and sintered; successive coats may be built up on the wire effectively increasing the diameter of the wire. The wire may be worked, as by swaging or drawing, to reduce its diameter. If desired, the process may be repeated. In this way, wire production from metal powder can be made to be continuous without resorting to the ingot and fabrication steps now employed.

The invention will best be understood from the following detailed description and the accompanying drawings, in which:

FIG. 1 is a schematic diagram of one arrangement of apparatus for the continuous slip forming of wire;

FIG. 2 is an etched and magnified cross-section of slipformed molybdenum wire;

FIG. 3 is an etched and magnified cross-section of slipformed molybdenum wire after swaging; and

FIG. 4 is an etched and magnified cross-section of slip- -formed molybdenum wire after swaging and drawing.

Referring to FIG. 1 there is shown schematically the apparatus for the continuous slip-forming of the wire. The wire 1 to be coated comes on a reel 2, and passes through a slack adjuster 3. It then passes through a slurry or slip made from a metal powder, as described below, contained in a slip applicator 4 wherein it is coated with the slurry.

The coated wire is then dried in the air-drying furnace 5 and sintered in the sintering furnace 6. Upon emerging from the sintering furnace 6 the coated and sintered wire is cooled in the heat exchanger 7 and is then withdrawn from the slip-forming apparatus.

If it is desirable to buildup a second or additional coats of slip on the wire, the wire may then be passed again through the preceding equipment by drawing the wire emerging from the heat exchanger 7 over pulleys 8, 9, 10 and 11 so as to make a second pass through the slip applicator 4, the air-drying furnace 5, the sintering furnace 6, and the heat exchanger 7. After the necessary number of coats have been built up on. the wire in this manner, it is drawn through the slack adjuster 12 onto the reel or winding head 13.

The slurry comprises a metal powder suspended in a liquid vehicle, such as water. By way of example, a suitable slurry for slip-coating of wire may consist of a water-metal powder slurry having a ratio of one part by weight of water to four parts by weight of metal powder. Slip-coats have been made having between two and up to ten parts of metal powder by weight to one part of water. The metal powder-water slurry is directly applicable or special additives (such as wetting agents, defiocculating agents and the like) may be added to impart specific desirable properties to the slip. For the application of the slip-forming of molybdenum wire, it Was found useful, but not necessary, to use a slurry containing an anionic deflocculating agent. It was found that regardless of the pH of the slurry from very acid to very basic, adequate coverage was provided when the slip was applied as a coating to the wire.

The coating on the wire may be sintered as well known in the art; a sintering temperature of 1900 C. produces good results, however, satisfactory results may be obtained in the range of about 1400 C. to 2000 C. The sintering furnace 5 preferably contains a non-oxidizlng atmosphere, such as a hydrogen atmosphere.

FIGS. 2, 3 and 4 illustrate a wire formed by the above process. A molybdenum wire of 0.048 inch in diameter was coated continuously to 0.060 inch in diameter by successive applications of molybdenum metal-powder slip. The coating on the wire was sintered at 1900 C. in a hydrogen atmosphere to insure adequate consolidation and adherence to the "base wire. FIG. 2 represents the cross-section of the slip-formed molybdenum wire after it has been thus coated from 0.048 to 0.060 inch diameter and sintered at the said 1900 C. in the hydrogen atmosphere. As is apparent from this figure, the porosity of the coating is very great. The base molybdenum wire 14 is seen to contain powdered metal coating particles 15; however, large voids 16 exist in the coating.

After coating, the wire has swaged to 0.048 inch diameter. This wire is illustrated in FIG. 3. It is seen that the porous coating has been considerably consolidated and that the voids 16 have been reduced.

The 0.048 inch diameter wire was then drawn to 0.010 inch diameter, a cross-section of which is shown in FIG. 4. The coating in FIG. 4 is no longer apparent and the wire looks much like that of an uncoated wire.

Similar sections of coated and sintered wire were also satisfactorily drawn directly from 0.060 to 0.010 inch diameter. While the above example illustrates the coating of molybdenum refractory metal powder on molybdenum base wire, tungsten wire has also been so formed. Likewise large molybdenum rod in the range of 0.10 to 0.50 inh diameter have been slip-coated and swaged satisfactorily to smaller sizes after the coating has been dried and sintered onto the rod sources. It is, of course, not necessary that the coating metal be the same as the base metal; for example, a coating of molybdenum can be secured to a tungsten wire by the above disclosed process. Also, while the above examples have referred to tungsten and molybdenum, the method according to the present invention may be advantageously used with tungsten 'base alloys, molybdenum base alloys and other metals.

One of the major advantages seen in this invention is that slip-forming of wire is considerably more economical than the present commercial process for the formation of wire. The process herein disclosed will save time, labor and materials. Specifically the process provides for a shorter and improved procedure for the formation of wire directly from metal powder without resorting to the normal practice of producing ingots and working these ingots to wire by rolling, swaging and drawing.

While many modifications may occur to those skilled in the art, the invention is to be limited only by the claims annexed to and forming a part of this invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A method for the production of refractory metal wire free from voids comprising the steps of coating a base wire selected from the group of tungsten, molybdenum, tungsten base alloys and molybdenum base alloys with a slurry having between 2 to 10 parts metal powder by weight of the same metal as the base wire to one part of water, drying the coating, sintering the coating at a temperature in the range of 1400 C. to 2000" C. in a nonoxidizing atmosphere, and working the sintered wire down to a diameter less than the original diameter of the base wire to consolidate the wire.

2. A method for the production of refractory metal wire free from voids comprising the steps of coating a base wire selected from the group consisting of tungsten, molybdenum, tungsten base alloys and molybdenum base alloys with a slurry having a ratio of 4 parts by weight of metal powder'of the same metal as the base were to one part by weight of Water, sintering the coating at about 1900 C. in a hydrogen atmosphere to adhere the coating to the base wire, and working the sintered wire down to a diameter less than the original diameter of the base wire to consolidate the wire.

3. A method .for the production of wire according to claim 2 wherein the base wire and slurry are of tungsten.

4. A method for the production of wire according to claim 2 wherein the base wire and slurry are of molybdenum.

References Cited in me file of this patent UNITED STATES PATENTS 1,547,395 Hoyt July 28, 1925 1,565,724 Fonda Dec. 15, 1925 1,617,161 Koref Feb. 8, 1927 1,723,862 Jacoby Aug. 6, 1929 2,339,392 Garner Jan. 18, 1944 2,667,429 Diffenderfer Jan. 26; 1954 10 2,854,732 Hessenberg Oct. 7, 1958 OTHER REFERENCES 15 New York, pages 59.1 and 627 relied on. 

1. A METHOD FOR THE PRODUCTION OF REFRACTORY METAL WIRE FREE FROM VOIDS COMPRISING THE STEPS OF COATING A BASE WIRE SELECTED FROM THE GROUP OF TUNGSTEN, MOLYBDENUM, TUNGSTEN BASE ALLOYS AND MOLYBDENUM BASE ALLOYS WITH A SLURRY HAVING BETWEEN 2 TO 10 PARTS METAL POWDER BY WEIGHT OF THE SAME METAL AS THE BASE WIRE TO ONE PART OF WATER, DRYING THE COATING, SINTERING THE COATING AT A 